You can add salt if you feel like it,it may help prevent fungus and other things but it doesn't really benefit their growth or anything like that. Thing is,if you add salt to guppy fry,platy's or sword's fry they tend to be dependant on it thru their lives. It's just a matter of personal choice. I myself add salt to everything,except the 10 gallon snail breeding tank,I don't muck with that.
well, i know that batch died and all, but now she had another one! just a few weeks later
this batch is healthy and happy..growing VERY fast
thanks all
sconrad